An electrolyte is a substance whose aqueous solutions or melts contain freely mobile ions which migrate toward the electrodes when an electric voltage is applied. Electrolytes can be used, for example, for electrochemical MCrAlY coating (M stands for nickel, cobalt, etc.; Y stands for yttrium and/or rhenium; silicon, hafnium, tantalum may also be present). MCrAlY coatings are usually used as thermally stable corrosion and oxidation protection, in particular in stationary gas turbines for generating energy and in the field of engines for aircraft and other means of transport.
Thermal spraying processes are mainly used of the coating. However, in this coating process it is usual for up to 70% of the metal powder not to be applied to the component. This metal powder therefore represents what is known as a waste product which, although in principle of high value, according to environmental guidelines has to be disposed of as a hazardous material or a substance which is harmful to health.
Used electrolytes containing high concentrations of the corresponding metals are produced during chemical or electrochemical removal or what is known as stripping of MCrAlY layers as part of the repair and refurbishment of gas turbine components. These electrolytes are in some cases classified as carcinogenic and/or toxic in other ways, and consequently solutions thereof usually have to be evaporated down in order to reduce their weight and then disposed of in a complex and expensive way as electroplating slurry containing heavy metals.
In general, the surface treatment of metals, both in electroplating technology and in material-removing processes, such as pickling, etching, pyrolysis, etc., and also the processing of metal-containing substances from chemistry, metallurgy and environmental technology produce process solutions with high levels of cations of the dissolved metals or disruptive foreign metals. On account of these high levels of metals, solutions or used electrolytes of this type have only a limited service life and uptake capacity. The renewal of baths of this type, which is periodically required, entails considerable outlay, both for replacing the chemicals used and for treatment and disposal of the used process solutions in a manner which complies with environmental regulations.
It is therefore desirable to at least reduce or even completely eliminate the costs of disposing of used electrolytes and waste produces which may form in the abovementioned processes and at the same time to keep the outlay associated with the provision of staring substances for producing a ready-to-use electrolyte at a particularly low level.